Embodiments relate to an inner-focusing type telephoto lens system used in digital still cameras or digital video cameras.
Recently, as demand for interchangeable lens digital cameras increase, image sensors such as a charge coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) used in digital cameras have a high pixel resolution with developments in technology.
In order to complement the high resolution image sensors, a lens used in an interchangeable lens digital camera should have excellent optical properties and a compact size for portability.
Also, most interchangeable lens digital cameras that have been recently released have a basic movie shooting function and require rapid and precise focusing during movie shooting. In order to satisfy the rapid and precise focusing of the interchangeable lens digital cameras, the interchangeable lens digital cameras need to have a light-weight focusing lens group capable of moving according to a location of an object.
Conventionally, a double Gauss type optical system is mainly used as a single focus semi-telephoto lens having an F-number equal to or less than about 2.0 in an interchangeable lens digital camera. Although it is possible to effectively decrease spherical aberration that is a major problem in a large aperture lens system via the double Gauss type optical system, performance of the double Gauss type optical system is deteriorated due to occurrence of a coma flare. Also, the double Gauss type optical system generally is based on the movement of an entire lens group, for correction of a change of image surface according to a variation in a location of an object, and thus the weight of a focusing group is increased, thereby decreasing focusing speed.